ISP Equipment and Where the Problem Actually Is
Why this matters
When a connected device you installed drops offline, the customer calls you, because your name is on the sticker. Often the device is fine, the home network is fine, and the internet service coming into the house is what failed. Other times the internet is fine and something inside the house broke. The two look identical from the app ("device offline"), and they have different owners: the internet provider (the ISP, internet service provider) fixes one, the customer or you fix the other. A tech who can tell them apart in five minutes saves a wasted repair, and saves the customer an hour on hold with the wrong company.
This card names the equipment you will find, who owns each piece, and the short sequence of tests that locates a fault.
The chain from the street to the device
Every home internet connection is a chain. Signal arrives from the provider's network on a cable, a fiber, a phone line or a radio, and ends at a device on the customer's Wi-Fi. Each link has its own box, though several can live in one housing.
The modem turns the provider's signal into an ordinary network connection. Its form depends on the service:
- Cable: a modem on the coaxial cable, the same kind of round cable a TV used.
- Fiber: an ONT (optical network terminal), usually a small box on a wall near where the fiber enters, sometimes with a separate power supply and backup battery.
- DSL: a modem on a phone line.
- Fixed wireless or cellular home internet: a receiver, often on a window or the roof, or a cellular gateway on a shelf.
The router creates the home network: it hands out addresses to devices, broadcasts the Wi-Fi, and sends traffic out through the modem. It is the boundary between "the internet" and "the house."
The gateway is a modem and a router in one housing. Most providers rent one by default. This is the source of most confusion, because the customer calls it "the router," "the modem" and "the Wi-Fi box" interchangeably, and it is all three.
Mesh nodes are additional Wi-Fi units spread through the house, linked to a main unit. They extend the Wi-Fi; they do not change the internet connection. See related: Mesh Systems, Extenders and Dead Zones.
Who owns what, and why it changes who you call
| Piece | Usual owner | Who services it |
|---|---|---|
| Line to the house, outside box | Provider | Provider only |
| Fiber ONT | Provider | Provider |
| Rented gateway | Provider | Provider; settings may be customer-changeable |
| Customer-bought modem or router | Customer | Customer, or you if hired |
| Mesh system | Customer, sometimes provider | Whoever bought it |
| Connected devices | Customer | You, if you installed them |
Ownership matters because you should not change settings on equipment the customer does not own without their authorization, and on provider equipment some settings are locked or reset by the provider remotely. A provider can push an update to its own gateway overnight that changes behavior in the house, which is one reason "it worked last week" calls cluster after provider maintenance. Changing anything on the customer's network is its own decision with its own sign-off; see related: The Customer Network Change Authorization SOP.
Hazard, at the outside equipment and the ONT: the outside box where the provider's line enters the house is the provider's demarcation point, and the line there may be on a pole or a buried run carrying signal you do not own; you do not open, disconnect or re-route it. On fiber, never look into the end of a disconnected fiber cable or the port on an ONT, because the light in it can be invisible and can injure an eye (the hazard IEC 60825-2 addresses for fiber systems). If the fiber or the outside box looks damaged, the customer calls the provider.
The four questions that locate a fault
Work these in order. Each one cuts the chain roughly in half.
1. Is it one device, some devices, or everything? Open the apps or ask the customer. One device offline points at that device or its spot in the house. Several devices offline in one area points at Wi-Fi coverage there. Everything offline at once points at the router, the modem or the provider.
2. Does a phone on the home Wi-Fi actually have internet? This is the question that gets answered wrong. Most phones quietly switch to cellular data when the Wi-Fi has no internet, so "my phone works" means nothing. Have the customer turn cellular data OFF on the phone, stay on Wi-Fi, and load a web page. If it loads, the internet and the router are fine and the problem is closer to the device. If it does not, keep going.
3. Can the phone reach the router at all? If the phone shows it is connected to the home Wi-Fi but cannot load a page, the router is up and handing out connections. The break is between the router and the internet. Most router and gateway apps show a status like "connected to internet" or "no internet connection" that answers this directly.
4. What do the modem's lights and status say? Every modem and gateway has a light or a status screen for its connection to the provider, usually labeled "online," "internet," "WAN" or with a globe icon. A solid normal color means it has a connection to the provider; blinking, off, or a warning color usually means it does not. Read the manual or the provider's support page for what each light means on that model, because colors are not standardized. The provider's outage page, checked on cellular data, often confirms a known outage.
A fault located at question 4, with the modem showing no connection, belongs to the provider.
Double routing, the self-inflicted problem
A customer who bought their own mesh system or router and plugged it in behind the provider's gateway now has two routers in a row. Both hand out addresses, and traffic passes through both. This is called double NAT (NAT, network address translation, is how a router shares one internet connection among many devices).
It usually works for browsing and streaming. It commonly causes trouble with devices that need incoming connections or local discovery: camera recorders, some hubs, game consoles, devices you set up on one router that end up on the other. The tell is two different Wi-Fi names in the house, or devices on the same Wi-Fi name that cannot find each other.
The usual fixes are to put the provider's gateway in bridge mode (it stops routing and acts as a modem only) or to put the customer's mesh system in access point mode (it stops routing and only broadcasts Wi-Fi). Either is a change to the customer's network with consequences for every device in the house, so it is a scoped and authorized job, not a quick tweak.
Worked example: the shutoff hub that dropped every evening
A customer reported that the water shutoff your shop installed sent "hub offline" alerts most evenings, then "hub back online" an hour or two later. They were annoyed and wanted the hub replaced. They said the internet was fine: they streamed TV every evening with no trouble.
Question 1. The tech asked whether anything else showed offline at the same times. The doorbell app's history showed offline events matching the hub's on four of the last seven evenings, between about 7 p.m. and 10 p.m. Two devices, two different makers, same times. That makes a hub defect unlikely, because two unrelated devices do not fail together on schedule.
Question 2. The TV was streaming. But this house's TV was plugged into the gateway by a cable, and the customer's phone fell back to cellular every time the Wi-Fi lost internet. So "streaming was fine" did not test the internet, and "my phone was fine" did not either. The tech asked the customer to do the cellular-off test the next evening when the alert came in.
Question 3 and 4, the next evening. At 8:20 p.m. the hub alert arrived. The customer turned off cellular: the phone showed connected to the home Wi-Fi, no web page would load, and the gateway's app said "no internet connection." The gateway's "online" light was blinking instead of solid. The TV was buffering. At 9:35 p.m. the light went solid and everything came back. The tech also asked the customer to open the gateway's status page, which logged several "lost connection to provider" events at matching times over the past week.
The location: the router was up, the Wi-Fi was up, and the gateway lost its connection to the provider. The hub was reporting correctly every time. Replacing it would have changed nothing, and the next alert would have followed the new hub.
What the tech did: wrote the evidence down for the customer to give the provider: dates and times of each drop, the blinking light, the status page entries, and that it happened with every device, wired and wireless. Evening drops on a cable service often point at a problem on the line or in the neighborhood that the provider must find. With a dated log, the provider's support call starts at "send a technician" rather than "have you tried restarting it."
The bill: a short diagnostic visit, under the shop's scope line for network work. The provider sent a technician who replaced a corroded connector outside the house, which the tech never touched. The alerts stopped.
What would have flipped it: if, during the evening drop, the phone with cellular off had loaded pages fine and only the hub showed offline, the fault would have been inside the house: the hub's Wi-Fi signal, the hub, or a router setting. That points to a different sibling; see related: The Device Keeps Dropping Offline.
The mistake this card exists to prevent
The expensive error is replacing a working device because it reported a real problem it did not cause. Connected devices are the most honest instruments in the house about the internet connection, because they notice every drop and report it. A shop that treats every offline alert as a device fault will replace good equipment, fail to fix the problem, and own the customer's frustration as well. Run the four questions first, with the phone on Wi-Fi and cellular off, before ordering a part.
References
- See related: Mesh Systems, Extenders and Dead Zones
- See related: The Customer Network Change Authorization SOP
- See related: The Device Keeps Dropping Offline
- See related: Restarting a Home Network in the Right Order
- IEC 60825-2, safety of optical fiber communication systems (the basis for never viewing a live fiber end or port)